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THE IB SAYS
THE IB SAYS
Essential idea: All waves can be described by the same sets of mathematical ideas. Detailed knowledge of one area leads to the possibility of prediction in another.
Understandings: Reflection and refraction; Snell’s law
Applications and skills: Sketching and interpreting incident, reflected and transmitted waves at boundaries between media ;Solving problems involving reflection at a plane interface; Solving problems involving Snell’s law
Utilization: Applications of the refraction and reflection of light range from the simple plane mirror through the medical endoscope and beyond. Many of these applications have enabled us to improve and extend our sense of vision.
Guidance: Quantitative descriptions of refractive index are limited to light rays passing between two or more transparent media. If more than two media, only parallel interfaces will be considered.
Data booklet:
My vodcast
My vodcast
Reflection
Reflection
Reflection is the change in direction of a wave when it meets a boundary / interface. This applies to all waves, including light, sound and water.
The law of reflection states that the angle of incidence is equal to the angle of reflection. These angles are drawn from the ray representing the waves to the normal. The normal is a line drawn perpendicular to the boundary at the point where the ray meets the boundary.
Refraction and Snell's Law
Refraction and Snell's Law
Refraction is the bending of a wave's path due to changes in the speed of a wave. The angle of refraction can be calculated using Snell's law (as given in the data booklet). The ratio of the sin of the angles is equal to the ratio of the speed of the wave in the two media. When moving from a faster medium to a slower medium the wave will bend towards the normal, and vice versa.
For light in transparent media we can define an absolute refractive index (n) which is the ratio of the speed of light in a vacuum to the speed of light in that medium.
Experimental determination of refractive index
Experimental determination of refractive index
The easiest way to determine the refractive index of a material (for light) is to shine a ray of light into the material and compare the angle of incidence to the angle of refraction. Then divide the sine of the incident angle by the sine of the refracted angle.
Refraction Interactive Simulations
Refraction Interactive Simulations
For the wonderful folk at PhET, the link is here or embedded below:
The great Walter Fendt also has an interactive simulation of reflection and refraction. This version explains the process using Huygens's Principle.
Resources from textbooks
Resources from textbooks
Oxford Physics: pages 145 - 148, including multiple worked examples on pages 147 - 148
Hamper HL (2014): pages 173 - 175 for water waves, 186 - 187 for light waves
Relevant questions from Dot Point Physics (4 Oscillations and Waves)
Relevant questions from Dot Point Physics (4 Oscillations and Waves)
Pages 205 - 209. Good practice questions and strongly recommended!
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